Test for Charpy Impact Resistance of Notched Specimens of Plastics ASTM D6110
ASTM D6110, The Charpy Impact Test, measures the energy absorbed by a plastic specimen while breaking under an impact load. A pendulum is used to break the plastic specimen. After a clean break, the energy loss of the pendulum due to the impact is recorded.
The results from ASTM D6110 are used to choose a suitable plastic for manufacturing products. They are also used for quality control which ensures that the quality of the product is maintained or improved; poor quality materials/products are discarded by the manufacturer.
The results of the Charpy Impact Test can also be used to determine the ductility of a material. If the material breaks on a flat plane, the fracture is brittle, and if the material breaks with jagged edges or shear lips, then the fracture is ductile.
In ASTM D6110, a notch is made in the plastic specimen with a milled notch. The notch produces a stress concentration, a part where the stress is greater than its surrounding area. This promotes a brittle fracture rather than a ductile fracture, minimizing plastic deformation, and directing the fracture behind the notch.
The machine used in ASTM D6110 has a pendulum-type hammer. The standardized plastic specimen is held securely at each end. The pendulum is pulled to a height and released. The hammer strikes opposite the notch and breaks the specimen into two. Because of the impact, the pendulum doesn’t swing as far. It has lost energy. That lost energy is the energy that was needed to break the plastic specimen. The specimen must break into two. Results from instances in which the pendulum doesn’t have enough energy to toss the specimen into two are not reported as a standard result.
Five standard plastic specimens are required with dimensions of 55 mm × 10 mm × 10 mm.
Along with a notch, the plastic specimen must have a standard length and a standard depth, although the width can be varied. The width dictates whether a brittle, low-energy break or a ductile, high-energy break will occur. Therefore, the width must be stated in the specification of the material.
Net Breaking Energy is calculated by subtracting the windage and friction loss energy from the indicated breaking energy.
Impact Resistance is calculated by Dividing the net breaking energy by the measured width of each specimen.
The average impact resistance for a group of specimens is calculated by adding the individual impact resistance values for the group and dividing the sum by the total number of specimens in the group.
The standard deviation is calculated as follows and reported in two significant figures: